The present invention relates to a pump, such as a vane-type pump or a roller-cell pump, in particular a transmission pump, having a double-stroke delivery contour, the delivery contour having at least one rise zone, at least one large circle region, at least one fall zone, and at least one small circle region, and, within the delivery contour, the pump having a rotor having radially displaceable vanes or rollers in radial rotor slots.
Pumps of this kind are generally known. The problem in this context is that transmission pumps are operated using foamed transmission oil. Due to the variation in the degrees of foaming, a great disparity in the oil elasticities results. If there is a high percentage of undissolved air in the oil, the oil is very soft. Thus, given a constant reversal geometry, the pressure equalization process takes longer than when working with hard, unfoamed oil, and longer rotation angles are required for the pressure reversal operation in order to react to the substantial variance in elasticity. These rotation angles are ultimately formed by the large circle region, whose angle is only slightly greater than the vane pitch. In this region, the cell volume is virtually constant (apart from the “fall”, that is a slight reduction in the vane displacement radially inwardly as a function of the rotation angle), and by using pressure equalization slots or intermediate capacities (see German Patent Application DE 100 27 990 A1), the pressure reversal can be realized gradually in small pressure increase gradients. However, these measures do not suffice for applications in which foamed transmission oil is used.